208 NATURE, OC'CITRRENCE, AND ORIGIN OF ALUNOGEN. 



portions of it on being viewed in a certain position by re- 

 flected light show a decided pink tinge. Most of the material 

 is columnar, but some of it is mealy in character. 



The alum probably originated from the attack of 

 sulphur dioxide on the fel spathic material in the trachyte 

 breccia which plugged up the vent through which the magma 

 was effused. Sulphur dioxide is a very common mineraliser 

 gas associated Avith acid magmas. As the plug of the 

 material has been weathered down, the sulphate has become 

 more concentrated and where protected from the weather 

 in the floor of the caves and along cracks it has crystallised 

 out in the forms found to-day. 



Quite recently Mr. E. C. Saint Smith* has reported on 

 an occurrence of natural alum at Boonmoo Pinnacle, about 

 80 miles south-west from Cairns. The material occurs 

 through the altered acid lava forming the iipper portion 

 of the pinnacle. Mr. Saint Smith states that the lava is 

 composed essentially of quartz and felspar with fairly 

 abundant iron pyrites, and that the fel spars have been very 

 largely kaolinised. It is distinctly probable therefore, that 

 the alum results from the attack of the products of alter- 

 ation of the pyrites upon the kaolin. 



New South Wales Alum Occurrences. 



In NeAv South Walesf it is found as a deposit from a 

 volcanic vent at Mt. Wingen, and as an efflorescence in 

 caves and under sheltered ledges of the Coal Measure 

 sandstone, usually A^th epsomite, at Dabee, Wallerawang 

 and Mudgee Road, the mouth of the Shoalhaven River, 

 and other places. It is also found in crevices in blue slate 

 at Alum Creek and at Gibraltar Rock. 



To Mr. R. Graff, B.Sc, my best thanks are due for 

 carrying out the very useful analyses of the alunogen 

 incrustation and the sandstone behind it. 



*Q'land Govt. Min. Journal, xix, p. 66. 



tMerrill, Non Metallic Minerals, 1910 Ed., p. 354. 



